/*
 * Copyright (C) 2007 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import static com.google.common.base.Preconditions.checkArgument;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.VisibleForTesting;

/**
 * Implementation of {@code Multimap} that uses an {@code ArrayList} to store
 * the values for a given key. A {@link HashMap} associates each key with an
 * {@link ArrayList} of values.
 * 
 * <p>
 * When iterating through the collections supplied by this class, the ordering
 * of values for a given key agrees with the order in which the values were
 * added.
 * 
 * <p>
 * This multimap allows duplicate key-value pairs. After adding a new key-value
 * pair equal to an existing key-value pair, the {@code ArrayListMultimap} will
 * contain entries for both the new value and the old value.
 * 
 * <p>
 * Keys and values may be null. All optional multimap methods are supported, and
 * all returned views are modifiable.
 * 
 * <p>
 * The lists returned by {@link #get}, {@link #removeAll}, and
 * {@link #replaceValues} all implement {@link java.util.RandomAccess}.
 * 
 * <p>
 * This class is not threadsafe when any concurrent operations update the
 * multimap. Concurrent read operations will work correctly. To allow concurrent
 * update operations, wrap your multimap with a call to
 * {@link Multimaps#synchronizedListMultimap}.
 * 
 * @author Jared Levy
 * @since 2010.01.04 <b>stable</b> (imported from Google Collections Library)
 */
@GwtCompatible(serializable = true)
public final class ArrayListMultimap<K, V> extends AbstractListMultimap<K, V> {
    // Default from ArrayList
    private static final int DEFAULT_VALUES_PER_KEY = 10;

    @VisibleForTesting
    transient int expectedValuesPerKey;

    /**
     * Creates a new, empty {@code ArrayListMultimap} with the default initial
     * capacities.
     */
    public static <K, V> ArrayListMultimap<K, V> create() {
        return new ArrayListMultimap<K, V>();
    }

    /**
     * Constructs an empty {@code ArrayListMultimap} with enough capacity to
     * hold the specified numbers of keys and values without resizing.
     * 
     * @param expectedKeys
     *            the expected number of distinct keys
     * @param expectedValuesPerKey
     *            the expected average number of values per key
     * @throws IllegalArgumentException
     *             if {@code expectedKeys} or {@code expectedValuesPerKey} is
     *             negative
     */
    public static <K, V> ArrayListMultimap<K, V> create(int expectedKeys,
            int expectedValuesPerKey) {
        return new ArrayListMultimap<K, V>(expectedKeys, expectedValuesPerKey);
    }

    /**
     * Constructs an {@code ArrayListMultimap} with the same mappings as the
     * specified multimap.
     * 
     * @param multimap
     *            the multimap whose contents are copied to this multimap
     */
    public static <K, V> ArrayListMultimap<K, V> create(
            Multimap<? extends K, ? extends V> multimap) {
        return new ArrayListMultimap<K, V>(multimap);
    }

    private ArrayListMultimap() {
        super(new HashMap<K, Collection<V>>());
        expectedValuesPerKey = DEFAULT_VALUES_PER_KEY;
    }

    private ArrayListMultimap(int expectedKeys, int expectedValuesPerKey) {
        super(Maps.<K, Collection<V>> newHashMapWithExpectedSize(expectedKeys));
        checkArgument(expectedValuesPerKey >= 0);
        this.expectedValuesPerKey = expectedValuesPerKey;
    }

    private ArrayListMultimap(Multimap<? extends K, ? extends V> multimap) {
        this(
                multimap.keySet().size(),
                (multimap instanceof ArrayListMultimap) ? ((ArrayListMultimap<?, ?>) multimap).expectedValuesPerKey
                        : DEFAULT_VALUES_PER_KEY);
        putAll(multimap);
    }

    /**
     * Creates a new, empty {@code ArrayList} to hold the collection of values
     * for an arbitrary key.
     */
    @Override
    List<V> createCollection() {
        return new ArrayList<V>(expectedValuesPerKey);
    }

    /**
     * Reduces the memory used by this {@code ArrayListMultimap}, if feasible.
     */
    public void trimToSize() {
        for (Collection<V> collection : backingMap().values()) {
            ArrayList<V> arrayList = (ArrayList<V>) collection;
            arrayList.trimToSize();
        }
    }

    /**
     * @serialData expectedValuesPerKey, number of distinct keys, and then for
     *             each distinct key: the key, number of values for that key,
     *             and the key's values
     */
    private void writeObject(ObjectOutputStream stream) throws IOException {
        stream.defaultWriteObject();
        stream.writeInt(expectedValuesPerKey);
        Serialization.writeMultimap(this, stream);
    }

    private void readObject(ObjectInputStream stream) throws IOException,
            ClassNotFoundException {
        stream.defaultReadObject();
        expectedValuesPerKey = stream.readInt();
        int distinctKeys = Serialization.readCount(stream);
        Map<K, Collection<V>> map = Maps
                .newHashMapWithExpectedSize(distinctKeys);
        setMap(map);
        Serialization.populateMultimap(this, stream, distinctKeys);
    }

    private static final long serialVersionUID = 0;
}
